Formation Of Deformation Bands Research Articles

Deformation banding in a precipitation hardened aluminum alloy during simple shear deformation

Simple shear deformation of a precipitation hardened aluminum alloy showed the formation of planar deformation bands on a set of parallel {111} planes. Band formation is more profuse in the near {101}[uvw] and {111}[uvw] oriented grains and their lateral growth is limited by the formation of special coincident site lattice boundaries. Irrespective of the parent grain orientation, these deformation bands are misoriented by approx. 40° with respect to the parent grain. The extended dislocations could not cross-slip, promoting planar slip and the formation of planar deformation bands upon persistent plastic deformation.

Can mechanical failure in unconsolidated sands during hydrocarbon production result in flow barriers?

Water injectors in unconsolidated sands often experience severe injectivity decline and premature failure. The formation of shear bands and compaction bands is a possible mechanism which can cause a flow barrier. Herein, we exploit an elasto-plastic bifurcation analysis in order to assess whether shear bands and compaction bands can form under realistic reservoir conditions. Since injection favors the formation of dilatant shear bands, we focus on the possible formation of compactant deformation bands during a preceding depletion period with the potential to severely impede flow during subsequent injection. A set of conditions is elaborated, and they indicate a low risk of localization as a consequence of hydrocarbon production. In fact, the possibility of localization reduces upon progressive depletion. An extensive sensitivity analysis shows that this conclusion continues to hold when varying the material parameters and initial stress conditions within a realistic range for subsurface conditions. This renders the sketched scenario of deformation bands acting as flow barriers unlikely under conditions typical of deepwater reservoirs in the Gulf of Mexico. The conclusion that localized deformation bands probably do not cause injectivity loss is reinforced since only compaction bands can reduce the permeability sufficiently to create effective flow barriers. They would form perpendicular to the major compressive principal stress, and in a normal faulting regime, this would result in bands with a low inclination angle to the horizontal plane. They would not adversely affect flow from or towards (vertical) wells in a reservoir.

Effects of pre-existing faults on compaction localization in porous sandstones

The formation of deformation bands can significantly modify the strength and transport properties of porous sedimentary rocks. Among the different types of deformation bands, compaction bands exhibit porosity reduction with little to no shear displacement. Natural compaction bands have previously been reported and studied in only a few areas. They often coexist with faults and other localized deformation structures. We mapped the geometrical relation between compaction bands, shear bands and faults in Lower Cretaceous porous sandstone at Makhtesh Katan, Israel. To understand the effect of pre-existing faults on the formation of compaction bands, we conducted deformation experiments on pre-faulted Bentheim sandstones. These experiments produced compaction bands consistently intersect the pre-existing fault. To gain better mechanical understanding of the observed band geometry, we also carried out three-dimensional (3D) numerical simulations with the input elastic moduli and yield strength well-constrained from the deformation experiments. We demonstrated that the formation of deformation bands is dictated by stress concentrations associated with the pre-existing fault. Frictional slip along the heterogeneous fault plane can produce a local stress concentration that would be responsible for further localized damage and the development of deformation zones. When fault slip is restricted (a possible result of high confinement), compaction bands initiate at high stress concentration sites resulting from geometrical irregularities of the fault. Finally, using a plane-strain two-dimensional (2D) linear-elastic model with the geometry of the faults mapped in the outcrop, we were able to provide a mechanical explanation of the distribution for deformation bands observed at the Makhtesh Katan study area.

SMA Constitutive Modeling Backed Up by 3D-XRD Experiments: Transformation Front in Stretched NiTi Wire

It has been known for a long time that martensitic phase transformation in NiTi shape memory alloys loaded in tension develops inhomogeneously via formation and propagation of macroscopic deformation bands resembling well-known Luders bands. Growing literature evidence supports the view that NiTi, in fact, develops a variety of localized deformation phenomena in particular geometries and loading modes. Coupling of cutting-edge experimental methods with dedicated modeling techniques can bring new insight into such a type of behavior. In this short review of our recent study, we demonstrate this synergic approach on the investigation of the martensite band in a stretched NiTi superelastic wire, in which the advanced technique of three-dimensional X-ray diffraction was complemented by NiTi-tailored constitutive model. We focus mainly on the modeling part, but the experimental background motivating and validating the chosen numerical approach is also briefly presented.

Physicochemical Processes Accompanying the Plastic Strain Localization under Pulsed Loading

The formation of localized deformation bands is accompanied by the mass transfer of particles of the matrix material (interstitial atoms, impurities, etc.) toward faults in the material being destroyed and by the emergence of stress oscillations in a mode of ultrasonic vibrations lasting several orders of magnitude longer than the initial pulse. It was assumed that dislocations generated under pulsed deformation are the cause of the migration of particles.

Determination of critical condition for initiation of dynamic recrystallisation in Zr-1%Nb alloy

The critical stress and strain for initiation of dynamic recrystallisation (DRX) in Zr-1%Nb alloy have been determined by employing two different approaches. The work hardening rate versus stress curve and the natural logarithm of work hardening rate versus strain were used for this analysis. To evaluate the onset of DRX in Zr-1%Nb alloy, the hot deformation behaviour of this alloy has been studied in the temperature range of 770–850 °C and strain rates range 10−2 to 1 s−1. To reduce friction during the tests, the ends of samples were coated with graphite powder and a thin layer of mica placed between the surface of samples and the anvils. Nevertheless, the flow stress values were corrected to eliminate the effects of friction and adiabatic heating during the tests. The outcomes of work hardening rate analysis showed that the first method (work hardening rate versus stress) is the best method to determine the critical conditions of initiation of DRX. All in all, for Zr-1%Nb alloy, the dynamic recrystallisation was found to start when the normalised stress and strain reach the values of 0.91 and 0.87, respectively. Furthermore, the transmission electron microscopy (TEM) analysis showed that the DRX took place through a continuous mechanism, and optical microstructures confirmed that at low temperature and high strain rate the flow curves could be explained by localised deformation and shear band formation.

Role of shear localization in nanocrystallisation of zircaloy-2 processed by wire rolling at cryo temperature

Shear localization during wire rolling of zircaloy-2 at cryo temperature has been investigated in the present work. Bulk nanocrystalline zircaloy-2 has been obtained by optimized annealing of cryorolled alloy. Microstuctural characterization and mechanical behavior of the processed alloy have been performed by X-ray diffraction (XRD), optical microscopy, Electron backscatter diffraction (EBSD), Transmission electron microscopy (TEM) and tensile testing. The presence of (ω) phase after wire rolling has been observed from XRD. The tensile strength of deformed zircaloy-2 (true strain = 2.77) was found to be 1015 MPa with a uniform ductility of 10.8%, while loss of tensile strength (837 MPa) and increase in ductility (14.8%) after annealing at 400 °C for 30 min were observed. Nanocrystalline structure with an average grain size of 30 nm has been formed after annealing at 400 °C for 10 min. The microstructure reveals the formation of shear bands during wire rolling at cryo temperature due to large applied strain in each pass. The possible mechanism of deformation and shear band formation has been discussed. The effect of strain rate on amount of work converted to heat (β) during shear band formation has been discussed. The calculation reveals that the rise in temperature during deformation was 831.6 °K on applying a strain of 2.77, during wire rolling at cryo temperature.

Effect of Annealing Temperature on Punching Shear Strength of Nb-A286 Superalloy

In the present research, effects of cold rolling and subsequent annealing on the microstructure and shear response of A286 superalloy were investigated. The present report has begun with a discussion on the alloy when it is cold-worked, with special emphasis on the formation of deformation bands. Next, following an annealing process in the temperature range of 900–1050 °C for 2–20 min, we have proceeded to depict static recrystallization, grain growth and precipitation phenomena. The mechanical properties evolution and the fracture surface analysis showed the occurrence of softening phenomenon in the temperature range of 900–950 °C as a result of either partial or full recrystallization. At 1050 °C, precipitation of Nb-rich phase caused an increase in ultimate shear strength of the alloy. Additionally, shear punch fracture surfaces of the samples annealed at 900–1000 °C represented dimple mode, with grain boundary decohesion being seen to occur at higher temperatures.

Effects of precipitates on microstructure evolution and texture in Mg-Zn alloy during hot deformation

The present research investigated ageing treatment on dynamic recrystallization and texture in Mg-Zn alloy by optical microscopy (OM), transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). Mg-6 wt.%Zn alloys were firstly solution and ageing treatment, and then the solutionized and peak-aged alloys were compressed at elevated temperature. The microstructure and texture were systematically investigated. Optical microstructure showed that ageing treatment prohibited dynamic recrystallization during deformation, which was because the precipitates inhibited dislocation movement and restricted the formation of deformation bands. The DRXed region and deformed region both contained typical basal texture with basal planes oriented perpendicular compression direction, but the recrystallized region showed a much weaker texture. The peak-aged alloy containing rod-shaped precipitates exhibited stronger texture intensity after dynamic recyrallization compared with the as-solutionized alloy, which was because the precipitates in the peak-aged alloy inhibited the lattice rotation of the newly formed DRXed grains or affected the microstructural evolution.

Microstructural and texture evolution of Jethete M152 flanged-test pieces during cold rotary forging

Rotary forging is an attractive incremental metal forming with many advantages over any other processes, requiring smaller deformation force and providing high accuracy (near-net-process). The main applications of rotary forging process include families of bevel and helical gears, and flanged components for transmissions such as disk, rollers, wheels, etc. The main aim of this work is to study the impact of rotary forging process on the microstructural and texture evolution of high-strength materials, and martensitic stainless steels in particular, during cold rotary forging process. Jethete M152 alloy is a cold formable 13%-Cr martensitic stainless steel used in the aerospace industry. Jethete M152 flanged test-pieces were rotary forged at room temperature. The process was interrupted at 4 intermediate steps, providing flange reductions of 25, 30, 50, 65 and 70%. A complex grain flow and inhomogeneous deformation patterns are developed during rotary forging, characterized mainly by the formation of a strong deformation band which run parallel to the bottom die. A transition from asymmetrical bulging (inverted mushroom) to symmetrical bulging was observed as a result of the initial lower contact area of the preform with the bottom die. From microstructural analysis by EBSD, the lath structure of Jethete M152 is gradually reoriented and changes it shape in a direction parallel to the compression plane, developing a lamellar/pancake structure in those positions with maximum deformation. These microstructural changes are accompanied with the development of a strong texture formed by a duplex (100)+(111) fibers aligned with the compression axis, being the (111) fiber the stronger one. These findings are in good agreement with uniaxial compression for bcc metals. The analysis of the Orientation Distribution Figures (ODF) reveals that 4 main texture components are formed in the course of the rotary forging process: Brass {110}(112), L {110}(110), I {112}(110), and Cube {001}(100). In contrast with the reported literature for bcc metals, no texture component associated to the γ-fiber ({111} ‖ ND) was found.

Strengthening in Al0.25CoCrFeNi high-entropy alloys by cold rolling

The effects of cold rolling on the evolution of microstructure and the mechanical behavior of Al0.25CoCrFeNi high-entropy alloys were investigated. Cold rolling resulted in extensive grain elongation, formation of deformation bands within the grains, and development of crystallographic textures that depended on the rolling reduction. The textures were investigated by electron backscattered diffraction after cold rolling. The present cold-rolled alloy indicates a strong brass-type texture. Cold rolling results in a substantial strengthening of the alloy; its ultimate tensile strength approaches 1479MPa, which was 2.8 times of that in the as-cast condition, but at the expense of low ductility (ε ~ 2.3%).

Deformation mechanisms of spherical cell porous aluminum under quasi-static compression

Quasi-static compression tests for a novel type of spherical cell porous aluminum prepared by the space-holder method were conducted. Formation and evolution mechanisms of deformation bands on the macro and micro scale were monitored and discussed by using a digital image correlation procedure. Effect of micro strain concentrations on the formation process and morphology of deformation bands at the macro level was analyzed in detail. In total three deformation modes of spherical cells and four failure modes of cell membranes including bending, shear, combined compression-shear, and eventually tearing were identified.

Cementation and structural diagenesis of fluvio-aeolian Rotliegend sandstones, northern England

Quartz cementation in sandstones is closely linked to grain coating phases and diagenetic alteration. Grain coatings consisting of illite–smectite stained with iron oxides and hydroxides are able to preserve large amounts of porosity by preventing the formation of syntaxial quartz overgrowth cement. The Penrith Sandstone Formation was chosen as an analogue for Rotliegend reservoirs to test the impact of grain coatings on quartz cementation. This adds to an existing model of cementation. Differences of grain coating coverage can be linked to grain size. Extensive grain coatings are present in finer grained laminae in some samples. Coarser grained laminae contain less extensive grain coatings. The analysis of grain coatings based on standard petrographic analyses is combined with high-resolution QEMSCAN® analyses. Structural features include deformation bands of different ages. Diagenetic alterations around faults, recorded by grain coatings, allow the delineation of relative temporal relations, revealing at least two generations of deformation band formation associated with normal faulting. In the Vale of Eden succession one normal faulting event postdates burial diagenetic quartz cementation as is evident by fault focused fluid flow and associated bleaching of iron and absence of quartz overgrowth.

Unified factor controlling the dislocation evolution of fatigued face-centered cubic crystals

By analyzing the formation mechanisms of different types of dislocation patterns, one unified factor is developed to account for effects of slip mode and further explore the basic law of dislocation evolution in fatigued face-centered cubic (fcc) crystals. First of all, in the formation of persistent slip band (PSB) ladders, geometrically necessary dislocations (GNDs) accommodate the elastic/plastic strain gradients between the hard walls and soft channels and provide the long-range internal stresses required for the simultaneous compatible deformation of soft and hard regions. In typical wavy-slip materials, advanced dislocation patterns include the wall, cell and labyrinth structures. The formation of deformation band (DB) walls may be derived from the accumulation of GNDs. The appearance of labyrinth and cell structures should be related to the activation of critical and coplanar secondary slip systems, respectively. In typical planar-slip materials, the dislocation structures consist of the dipole arrays and stacking fault (SF) bands. The constant compression of the split distance between partials will lead to the conversion of the closely spaced dipole array to the SF bands, which indicates that both wavy-slip and planar-slip materials follow one unified evolution factor. This factor, labelled α in this work, may be described as the ratio of the annihilation distance of screw dislocations to the split distance between partials, which can characterize the slip mode. The higher the α value is, the easier will be the appearance of PSBs and various advanced dislocation patterns. With decreasing the α value, dislocation evolution gradually changes from 3D patterns to 2D structures.

Effect of microstructural evolution on deformation behaviour of pre-strained dual-phase steel

The influence of microstructural evolution on the strain hardening and non-uniform deformation behaviour of pre-strained ferrite-martensite DP steel was studied using a crystal plasticity finite element method (CPFEM). The material parameters in the CPFEM were identified through a systematic procedure by fitting models to the experimental results of micro-tensile tests. The CPFEM with the identified parameters were applied to the analysis of virtual models with focus on the microstructural factors such as the angle of interphase boundary, the orientation of habit plane in the martensite phase, and the intensity of texture in the ultrafine-grained ferrite phase developed in the severely-deformed sample. The analysis results suggested the following influences of microstructural factors on the deformation behaviour. The formation of deformation bands in the ferrite phase depends on the configuration of the interphase boundary, the orientation of the habit plane in neighbouring martensite phase and the intensity of texture in the ferrite phase. The suppressions of the deformation bands by controlling microstructure could contribute to later onset of necking and resultant higher strain hardening.

Effect of thermomechanical processing on microstructural evolution and deformation behaviour of polycrystalline magnesium under quasi-static and high strain rate conditions

The effect of thermomechanical processing on microstructure evolution and room temperature flow behaviour of polycrystalline magnesium in compression at strain rates of ~10−2 and ~103 s−1 was investigated. Different initial microstructures were produced by optimising rolling and annealing cycles. Prior to annealing for 1 h at 350 °C, Mg samples were processed by two different treatments such as (i) hot rolling at 350 °C and (ii) hot rolling at 350 °C plus cold rolling at room temperature. Introduction of cold working step led to an increased fraction of hard oriented grains with a marginal grain size difference in post-annealed samples. A profound effect of thermomechanical processing on strain hardening rate as well as rate-sensitive flow behaviour of Mg was observed. The influence of prior processing history and strain rate on flow behaviour of Mg was clearly reflected in terms of texture strengthening/weakening phenomena and formation of microstructural deformation bands.

Dynamic compressive deformation behavior of SiC-particulate-reinforced A356 Al alloy matrix composites fabricated by liquid pressing process

In this study, A356 Al alloy composites reinforced with SiC particulates (SiCp), whose SiCp volume fraction was quite high (about 56vol%) for a candidate surface material of multi-layered armors, were fabricated by a liquid pressing process, and their dynamic compressive properties were investigated by using a split Hopkinson pressure bar. Defects such as misinfiltration or pores were eliminated, but about 2vol% of eutectic Si particles and about 3vol% of Fe-Al intermetallic compound particles were contained in the Al matrix. According to the dynamic compressive test results, dynamic compressive strength and strain were much higher than quasi-static ones because of strain-rate hardening effect and existence of molten Al matrix formed by adiabatic heating. The as-cast composite showed the best combination of dynamic strength and strain, together with the highest dynamic toughness, because the crack propagation was effectively blocked by the molten Al matrix and deformation band formation, while the T6-heat-treated composite showed the lowest compressive strain in spite of the highest strength. These findings suggested that the present Al-SiCp composites could be reliably applied to armors because the dynamic toughness or resistance to fracture was much higher under the dynamic loading than under the quasi-static loading.

Subsurface deformation in hypervelocity cratering experiments into high-porosity tuffs

Hypervelocity impact experiments on porous tuff targets were carried out to determine the effect of porosity on deformation mechanisms in the crater's subsurface. Blocks of Weibern Tuff with about 43% porosity were impacted by 2.5 mm and 12.0 mm diameter steel spheres with velocities between 4.8 km s−1 and 5.6 km s−1. The postimpact subsurface damage was quantified with computer tomography as well as with meso- and microscale analyses of the bisected crater subsurface. The intensity and style of deformation in mineral clasts and the tuff matrix were mapped and their decay with subsurface depth was determined. Subsurface deformation styles include pore space compaction, clast rotation, as well as microfracture formation. Evaluation of the deformation indicates near-surface energy coupling at a calculated depth of burial of ~2 projectile diameters (dp), which is in conflict with the crater shape, which displays a deep, central penetration tube. Subsurface damage extends to ~2 dp beneath the crater floor in the experiments with 2.5 mm projectiles and increases to ~3 dp for 12 mm projectiles. Based on overprinting relationships and the geometrical orientation of deformation features, a sequence of subsurface deformation events was derived (1) matrix compaction, (2) intragranular crack formation in clasts, (3) deformation band formation in the compacted matrix, (4) tensile fracturing.

Influence of mechanical stratigraphy on clastic injectite growth at Sheep Mountain anticline, Wyoming: A case study of natural hydraulic fracture containment

Sandstone injectites ranging from 1 km in outcrop length intrude the Cretaceous Mowry Formation in the vicinity of Sheep Mountain anticline (Bighorn Basin, Wyoming, USA). These injectites were sourced from the Peay Sandstone Member of the overlying Cretaceous Frontier Formation and represent a significant possible fluid pathway through impermeable shales. Sand injection occurred along dikes and sills, interacting with bedding discontinuities and preexisting joints in the Mowry Formation during the early folding of Sheep Mountain anticline. We argue that, in contrast to the passive sweeping of sediments into fissures characteristic of Neptunian dike formation, downward intrusion of the Peay sand was forceful and made possible by a highly stratified horizontal stress field resulting from the deposition, burial, and lithification history of the rock units in the area. The internal structure of the injectites is dominated by two sets of mutually offsetting deformation bands. The deformation bands have shear and compaction components, exhibiting significant porosity loss, as well as cataclasis and minor pressure solution. After formation of the deformation bands, subsequent faulting was localized along the margins of deformation bands, evidenced in the field by slickensided surfaces. A detailed kinematic analysis of slickenline lineations yields shortening and extension axes consistent with deformation band formation during early Laramide–oriented shortening, and continuing through the folding of Sheep Mountain anticline. Beyond the formation and deformation of these sandstone injectites, this study highlights the importance of mechanical stratigraphy in the containment of hydraulic fractures.

Localized deformation via multiple twinning in a Mg–Gd–Y–Zr alloy processed by high-pressure torsion

Different with common grain refinement dominated by dislocation activities, grain subdivision induced by sequential activation of multiple twinning was observed in a Mg-Gd-Y-Zr magnesium alloy via high-pressure torsion. Deformation bands were evolved from large primary twin bands, which contained refined grains through localized multiple twinning. Nanometer-scaled amorphous bands were also observed within deformation bands in Mg alloys for the first time. These observations indicate that localized deformation via multiple twinning and the consequent formation of deformation bands are potential routes to grain refinement in rare earth-magnesium alloys.